Why is muscle biopsy a valuable diagnostic tool in the evaluation of metabolic myopathies?
Muscle biopsy for routine histologic, histochemical, and ultrastructural analysis (electron microscopy) is helpful in evaluating a suspected metabolic myopathy, primarily because it helps rule out other conditions that can cause muscle dysfunction and allows testing for deficiencies or absence of specific glycolytic pathway enzymes. However, biopsy should be the final step in the clinical evaluation, done only if a diagnosis has not been made via history, examination, laboratory testing (including FET), genetic testing, and EMG. Specific enzymes can be tested for in muscle tissue by immunohistochemistry. The most important studies are listed below:
| Stain | Condition |
|---|---|
| Periodic acid-Schiff | GSD |
| Sudan black or Oil red O | Lipid storage diseases |
| Gomori | MM |
| Acid phosphatase | Acid maltase deficiency |
| Specific enzymes: | Myophosphorylase, phosphofructokinase, lactate dehydrogenase |
